Barcelona is the capital and most populous city of the Autonomous Community of Catalonia and the second largest city in Spain. It is the central nucleus of the Urban Region of Barcelona, which relies on a population of about 5.5 million. It is located on the Mediterranean coast between the mouths of the rivers Llobregat and Besòs and is limited to the west by the Serra de Collserola ridge (512 m/1,680 ft).